Alkali metal oxides commonly exist as impurities or promoters in syngas conversion catalysts and can significantly influence the activity and selectivity towards higher oxygenate products. In this study, we investigate the effects of sodium oxide on silica-supported Rh catalysts by experimentally introducing different amounts of sodium and monitoring the change in reactivity and CO adsorption behavior. The experimental results combined with density functional theory (DFT) calculations show that sodium selectively blocks step/defect sites on Rh surfaces, leading to reduced activity but higher C-2 oxygenate selectivity. DFT calculations also suggest that sodium present on Rh terrace sites can facilitate CO dissociation, potentially increasing C-2 oxygenate production. The overall activity and selectivity toward various products can be changed significantly based on the degree of site blocking by the added sodium.